In friction welding pure aluminium and 0.45 % carbon steel of 16 mm diameter, suitable welding condition and some fundamental phenomena are investigated. The continuous drive type friction welding machine is used. Range of experimental condition is, rotation speed: 3600 rpm, heating pressure: 1.0-3.0 kg/mm2, upsetting pressure: 1.0-4.0 kg/mm2, heating time: 0.5-10.0 sec, upsetting time: 10.0 sec, Main results are as follows; (1) The joints, which has interfacial layer, break at the layer in tensile test. And they have the relatively lower tensile strength and crack initiation angle. Therefore, the interfacial layer lowers the property of the joint. (2) The condition, under which the interfacial layer is not generated, that is, the relatively higher heating pressure and upsetting pressure and the comparatively shorter heating time, can be suitable for welding of aluminium and carbon steel. (3) The interfacial layer is produced when the average temperature at the friction interface rises above some 500°C. (4) The interfacial layer consists of the intermetallic compounds, mainly, Fe2Al5 and FeAl3.
Effect of precipitates on austenite grain growth in weld-heat affected zone (HAZ) was investigated using AlN-bearing steel. That is, grain growth and the behavior of precipitates during rapid heating were examined. Then, grain size in HAZ was examined. In these cases, initial amount and size of precipitates were controlled by pre-heat treatment. Main results obtained are as follows. 1) During rapid heating If initial value for r/f (r:radius of precipitates, f: volume fraction of precipitates) is sufficiently large, the effect of precipitates on grain growth is little.If initial state of precipitates is large in amount and small in size, grains hardly grow untill precipitates begin to dissolve. But, as the dissolution is very.rapid, grains grow rapidly when precipitates begin to dissolve. On the other hand, when size of precipitates is large in the initial state, grains grow gradually before precipitates begin to dissolve. As the dissolution of precipitates is gradual, grains grow gradually even when precipitates begin to dissolve. 2) In weld-heat affected zone The same phenomenon as obtained during rapid heating was observed in HAZ, in regard to grain size. That is, if initial state of precipitates is large in amount and small in size, grain size near the fusion line is very coarse, but the grain coarsened zone is narrow. On the other hand, if initial state of precipitate is large in size, the grain coarsened zone is wide but the grain size near the fusion line is not so coarse.
In this study, diffusible hydrogen in electroslag weld metal changing the polarity was determined by IIW-hydrogen determination method after sampling from molten weld metal by vacuum quartz tube. Residual hydrogen was measured by hot vacuum extraction method at 650°C after diffusible hydrogen determination. The obtained results are as follows; 1) Hydrogen content in electroslag weld metal is not influenced by welding polarity, welding current and basicity of flux. 2) Hydrogen content in electroslag weld metal decreases as the increase of CaF2 contents in flux. 3) Hydrogen distribution in electroslag welded joint was higher content at the starting part and lower content at the end part.
In the previous study, the welding condition for preventing the transverse weld cracking in submerged-arc welding of HT-80 were determined. In the present study, y-groove cracking tests were employed for determining the root cracking condition. The root cracking characteristics depend on the PCM of base metal or weld metal, whichever is higher, diffusible hydrogen content of weld metal and cooling time of weldment. The critical conditions to prevent the transverse cracking are severer than the ones to prevent the root cracking. It is concluded, therefore, that an adoption of the welding conditions to prevent the transverse cracking generally guarantees both the root and the transverse crack-free weldments in submergedarc welding of HT-80 steels.
Surface preparation of tungsten base sintered alloys (Ag-W, Cu-W alloy) was studied to improve the wetting of BAg filler metals. Several interesting results were obtained as follows. (1) The etching treatment of Ag-W or Cu-W sintered alloy in molten NaNO2 made the surface rich with silver or copper by selective dissolution of tungsten. The improvement of spreadability of BAg filler metals on Ag-W or Cu-W sintered alloy was gained by means of the etching treatment in molten NaNO2. (2) The addition of nickel metal to silver filler metal or to sintered alloys improved the spreadability a little with similar effect to the etcing treatment. (3) By the addition of CoCL2 or NiCL2 to the fluoride system flux, the spreadability was greatly improved, due to the deposition of Co or Ni from CoCL2 or NiCL2 on the surface of sintered alloy.
Effects of welding parameters (especially focus position of the beam and welding speed) on occurrence of defects (such as vertical cracks, root cracks and voids) in electron beam welds of heavy section Cr-Mo steel plates were investigated. Partial penetration welding in flat position, and 40 to 60 mm penetration depth were employed in this study. It was concluded that, (1) Correlations are found to exist at welding speed of 20 cm/min. among the bead shapes in cross sections, patterns of solidification ripple lines in vertical sections and tendency of occurrence of welding defects. These relations are not clear at 50 cm/min, because defects occurred too frequent at this speed. (2) Quantitative relations exist, at 20 cm/min. welding speed, between lags of solidication ripple lines in vertical sections and tendency of occurrence of welding defects. Welding defects are less likely to occur, when lag of solidification (C1 and C2) is small and solidification proceeds smoothly forward from the top of the bead to the bottom. (3) It is desirable to select slow welding speed and below the surface focus position ab≅0.5 to 0.6 at which a wedge shaped bead is obtained to avoid the above mentioned welding defects. In this case, the spikes become larger and some measures are required to avoid undesirable effects of spikes. (4) It is found that formation conditions of vertical cracks and voids, which have been discussed in this report, are very close, and differences of the bead shapes and the lags of solidification ripple lines decide whether voids or vertical cracks occur. It is more exact, in our opinion, to describe the vertical crack discussed in this report, as a shrinkage cavity which takes the form of a vertical crack.
The mechanism as to why stress-relief craking originates has been investigated from the standpoint of the residual stress. The results were obtained as follows : (1) The stress-relief cracking which occurs at the toes of the back side is closely related with the residual stress perpendicular to the weld line. Cracks arise when the residual stress exceeds 50 kg/mm2, whereas they do not appear at all under less than 50 kg/mm2. (2) In order to prevent the stress-relief cracking, it is advisable to select groove shapes and depositing methods with less than 50 kg/mm2 of the residual stress. (3) Whether or not the stress-relief cracking is caused is decided by the relation between the fracture stress of welded joints at the elevated temperature and the residual stress to the weld line after the stress-relieving.